The invention relates to closed-loop control systems, such as systems for controlling manufacturing processes.
Continuous feed manufacturing systems, such as manufacturing systems used to produce paper, film, tape, and the like, often include one or more motor-driven rotatable mechanical components, such as rollers, casting wheels, pulleys, gears, pull rollers, extruders, gear pumps, and the like. These systems often include electronic controllers that output control signals to engage the motors and drive the motors at pre-determined speeds. A typical controller often includes sophisticated closed-loop control circuitry that monitors the speed of the motor and adjusts the output signals to compensate for any detected error.
Nevertheless, the rotatable mechanical components of these systems tend to experience speed variations, often due to the other mechanical components coupling the motor to the rotatable mechanical component. For example, speed variations may be introduced by gear boxes, mechanical couplers, bearing friction, cogging torque, gain offset of sensors and other anomalies within the system. These speed variations during the manufacturing process can lead to imperfections or variations within the manufactured product. Accordingly, it is desirable to reduce or eliminate the speed variations such that the rotatable members can be driven as closely as possible to a desired velocity.
In general, the invention relates to adaptive closed-loop control techniques that reduce speed variations of precision-controlled rotatable mechanical components. In particular, the adaptive, closed-loop control techniques described herein can dynamically detect and reduce speed variations even though the speed variations may shift in amplitude, frequency and phase during the rotation. Exemplary rotatable mechanical components include, for example, rollers, casting wheels, pulleys, gears, pull rollers, extruders, gear pumps, and the like.
In one embodiment, the invention is directed to a system having a motor operable to drive a rotatable mechanical component in response to a motor control signal. A sensor generates a speed signal that represents the angular velocity of the mechanical component. The sensor may be, for example, a sine encoder mounted to a shaft of the mechanical component. A controller receives the speed signal, and generates a set of data elements based on the speed signal over one or more revolutions of the mechanical component.
In particular, the set of data elements relate speed variations of the mechanical component to a plurality of angular positions of the mechanical component. For example, the set of data elements may comprise angular velocity error data for the mechanical component at each of the angular positions. Alternatively, the controller may decompose the speed signal into frequency components, and identify destructive frequencies. In that case, the set of data elements may comprise frequency, amplitude and phase data for the components.
The controller continuously monitors the speed signal, updates the set of data elements, and adjusts the motor control signal based on the set of data elements. In this manner, the controller provides adaptive, closed-loop control of the mechanical component. The controller may, for example, generate an error signal based on the set of data values, and induce the error signal into closed-loop control circuitry as feedback to adjust the motor control signal. To generate the error signal, the controller makes use of a motor reference signal, such as a motor speed reference signal, a motor torque reference signal, or a motor position reference signal.
The controller maintains the set of data elements within a storage medium, such as a non-volatile random access memory (NVRAM), FLASH memory or the like. In particular, the controller may store the set of data elements as a lookup table (LUT) in which the data elements store angular velocity error data for the angular positions of the mechanical component. For example, the lookup table may comprise N*M data elements, where the N*M data elements store angular velocity data for N angular positions over M revolutions of the mechanical component.
The controller continuously updates the data elements in real-time to provide adaptive control and effectively reduce the speed variations. For example, for each angular position, the controller calculates an average velocity of the mechanical component over a subset of the proceeding angular positions, and subtracts the average angular velocity from a reference velocity to produce a current velocity error. The controller then updates the respective data element based on the current angular position of the mechanical component and as a function of the calculated velocity error.
In another embodiment, the invention is directed to a method comprising receiving a speed signal representing angular velocity of a rotatable mechanical component, and generating a set of data elements from the speed signal. The set of data elements relates speed variations of the mechanical component to a plurality of angular positions of the mechanical component. The method further comprises generating an error signal based on the set of data elements, and adjusting a motor control signal based on the error signal. The set of data elements may comprise angular velocity error data for the mechanical component at the angular positions. Alternatively, the data elements may comprise frequency, amplitude and phase data for frequency components of the speed signal.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.